In the past few years, in the refrigeration and air-conditioning industry, there is a growing movement to change a conventional refrigerant to a refrigerant having a low GWP (Global Warming Potential). Currently, as an alternative refrigerant (a next refrigerant) to R410A widely used in an air conditioner, R32, R290, R1234ze and the like are raised as candidate refrigerants.
A candidate refrigerant R32 has a problem that its molecular weight is small and leakage loss increases as compared with R410A. Further, candidate refrigerants R290 and R1234ze have a problem that their volumetric capacity is low as compared with R410A. As a solution to these problems, it is effective to reduce a displacement volume of a compressor and to operate the compressor in high-speed rotation.
However, when operating a scroll compressor in high-speed rotation, there is a possibility that by centrifugal force generated by an orbiting scroll or a motor (rotor), a crankshaft is bent, and reliability of a bearing for supporting the crankshaft is reduced or vibration noise is increased.
In order to avoid this phenomenon, it is necessary to use a lightweight material such as an aluminum-based material for the orbiting scroll. However, when using the aluminum-based material only for the orbiting scroll and using a conventional iron-based material for a fixed scroll, a gap inside the compressor is expanded due to a difference in linear expansion coefficient between the iron-based material and the aluminum-based material, to reduce efficiency. Therefore, it is desirable that a material of the orbiting scroll and a material of the fixed scroll are the same material.
Further, the fixed scroll compresses a refrigerant gas and is provided with a discharge port for discharging the refrigerant gas, and a release valve device for discharging the refrigerant gas at an early stage under the condition that liquid compression or pressure ratio is low. For example, Patent Document 1 describes this release valve device.